Mix together the meat, egg, bread crumbs, cheese, basil, parsley, and green onions; shape into 3/4 inch balls. Pour broth into a large saucepan over high heat. When boiling, drop in meatballs. Stir in escarole, lemon zest and orzo. Return to a boil; reduce heat to medium. Cook at a slow boil for 10 minutes or until orzo is tender, stirring frequently.
Place the olive oil in a deep pan and heat over medium-high heat. Stir in the onion, and cook until transparent, about 5 minutes. Mix in the carrots, celery, potatoes, zucchini, and leek. Stir and cook 5 minutes more. Pour in the hot water to cover the vegetables.